This program is planned to broaden our current knowledge of carcinogenesis by N-nitroso compounds in three main areas: (1) N-Nitroso compounds may be involved in the etiology of a significant fraction of human cancer. (2) N-Nitroso compounds are capable of inducing tumors in specific organs of experimental animals, which are difficult or impossible to induce by other carcinogens. (3) N-Nitroso compounds may act as carcinogens (at least in part) by alkylating cell macromolecules (e.g., DNA) in a fairly direct fashion, with or without prior enzymic activation.